Individual data line strobe-offset control in memory systems

ABSTRACT

Systems and methods for strobe signal timing calibration and control in strobe-based memory systems are provided below. These strobe-offset control systems and methods receive a strobe signal from a memory device and in turn automatically generate separate per-bit strobe signals for use in receiving data on each data line of a memory system. The systems/methods generate the optimal per-bit strobe signals by automatically calibrating per-bit offset timing between data signals of individual data bits and corresponding strobe signals. The strobe-offset control system effectively removes the detected phase difference between the data signal and the strobe signal.

RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.10/923,421, filed Aug. 20, 2004, now U.S. Pat. No. 7,171,321 andentitled INDIVIDUAL DATA LINE STROBE-OFFSET CONTROL IN MEMORY SYSTEMS,which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The disclosure herein relates generally to memory systems and methods.In particular, this disclosure relates to systems and methods fortransferring information among memory devices and a memory controller.

BACKGROUND

High-speed processor-based electronic systems have become all-pervasivein computing, communications, and consumer electronic applications toname a few. The pervasiveness of these systems, many of which are basedon multi-gigahertz processors, has led in turn to an increased demandfor the systems to host a larger number of applications having a higherlevel of complexity than those applications hosted on electronic systemsof previous generations. The transfer of information and signalsrequired among the components of these high-speed systems in support ofthese applications has led to increasing demands for interfaces tosupport the efficient high-speed transfer of information. Examples ofsuch interfaces include the interfaces between processors and memorydevices of high-speed systems.

One memory type typically used in high-speed processing systems isdouble-data rate dynamic random access memory (DRAM). The double-datarate DRAM is typically twice as fast as a single data rate DRAM runningat the same clock speed because a double-data rate DRAM transfers dataon both the rising and falling edge of the clock.

While the use of double-data rate memory systems leads to increases indata transfer speeds, issues arise regarding the timing of the datatransfer, particularly where a memory controller receives data sent by adouble data rate DRAM attached thereto using a strobe-based method.Using this strobe-based method, a strobe signal (also referred to as theDQS signal) is edge-aligned to and accompanies a data signal (alsoreferred to as the DQ signal) sent by the DRAM. This DQS is used by thecontroller to capture the data signal sent by the DRAM. The DQS signaland the data are received and the DQS signal is delayed by some fixedamount, usually one-fourth of the memory system clock period. Thisdelayed DQS signal, which is approximately in quadrature with thereceived data, is then used as a common sample clock for each of the DQinput receivers in typically a byte or 8 bits of data sent in parallel.Due to system offsets and pin-to-pin offsets in the DRAM (commonlyreferred to on DRAM datasheets as “tDQSQ”), however, one strobe-delayvalue for the whole byte cannot be the ideal amount of strobe-delay forevery pin. Furthermore, while manual adjustment of per-bit offsets canyield higher performing memory systems, requiring manual adjustments ofthese offsets in a production memory system tends to be expensive.

In some memory systems, calibration is performed by affecting the readand write timing positions of the memory controller based on patterncomparisons. For example, to calibrate the read timing of a system, aDRAM can be instructed to provide a known pattern to the controller. Thecontroller then adjusts its read-clock timing position to determine thepass-fail regions (e.g., when a comparison between the received data andthe expected data fails, the controller determines that phase positionto be in a fail region). Once the pass-fail regions for the entiredata-eye are known, the controller chooses an optimal read-clockposition centered within the known passing region. A strobe-delay valuecan be subsequently determined for this optimal read-clock position.

Timing-calibrated memory systems which eliminate pin-to-pin timingvariation can give better performance than strobe-based memory systemswhich use per-byte strobes, but they are substantially more complex.Consequently, there is a need in high-speed, strobe-based memorysystems, for per-pin (data bit) strobe-offset control and timingcalibration to minimize DQS-to-DQ timing offsets for each DQ pinindividually, yielding more robust, higher-speed systems.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, the same reference numbers identify identical orsubstantially similar elements or acts. To easily identify thediscussion of any particular element or act, the most significant digitor digits in a reference number refer to the Figure number in which thatelement is first introduced (e.g., element 120 is first introduced anddiscussed with respect to FIG. 1).

FIG. 1 is a block diagram of a strobe-based memory system including astrobe-offset control system for individual data line strobe-offsetcontrol, under an embodiment.

FIG. 2 is a flow diagram for individual data line strobe-offsetcalibration in a calibration mode, under an embodiment.

FIG. 3 is a flow diagram for receiving data signals of an individualdata line using an optimized sample signal, under an embodiment.

FIG. 4 is a block diagram of a strobe-based memory system including astrobe-offset control system in the calibration mode, under anembodiment.

FIG. 5 is a timing diagram showing the determination/application of theoptimal per-bit variable delay to a strobe signal to generate per-bitstrobe signals during calibration mode, under an embodiment.

FIG. 6 is a block diagram of a strobe-based memory system including astrobe-offset control system in the receiver mode, under an embodiment.

FIG. 7 is a timing diagram showing adjustment of strobe signal timingusing an optimal per-bit offset (calibration mode) along with a fixeddelay (receiver mode) to generate a per-bit strobe signal with optimalalignment for sampling a corresponding data signal, under an embodiment.

FIG. 8 is a block diagram of a strobe-based memory system including astrobe-offset control system for individual data line strobe-offsetcontrol, under an embodiment.

FIG. 9 is a block diagram of a delay element control circuit for use instrobe-based memory controllers, under an embodiment.

FIG. 10 is a block diagram of a strobe-offset control system forindividual data line strobe-offset control in strobe-based DDR memorysystems, under an alternative embodiment of FIG. 1.

FIG. 11 is a block diagram of a control system for individual data linerising and falling edge strobe-offset control in strobe-based DDR memorycontrollers, under an alternative embodiment of FIG. 10.

FIG. 12 is a block diagram of a calibration control circuit, under anembodiment.

FIG. 13 shows a charge pump that can replace the N-bit counter of acalibration control circuit, under an embodiment.

DETAILED DESCRIPTION

Systems and methods for strobe signal timing calibration and control instrobe-based memory systems are provided below. These systems andmethods, also referred to herein as strobe-offset control systems andmethods, receive a strobe signal from a memory device and in turngenerate separate per-bit strobe signals for use in receiving data on anexternal data line or signal line of a memory system. Thesystems/methods generate the optimal per-bit strobe signals byautomatically calibrating per-bit offset timing between data signalsDQ<X> of individual data lines (where DQ<X> represents any one of anumber of data lines DQ<N:0>, where X is any of data lines 0, 1, 2 . . .N) and corresponding strobe signals DQS. The strobe signals DQS are alsoreferred to as strobes and data strobes. The strobe-offset controlsystem is for use in strobe-based memory systems which include, forexample, double data rate (DDR) systems like DDR SDRAM as well as DDR2SDRAM and other DDR SDRAM variants, such as reduced latency DRAM(RLDRAM), RLDRAM2, Graphics DDR (GDDR) and GDDR2, GDDR3, but is notlimited to these memory systems.

The strobe-offset control system generally includes a calibrationcontrol circuit coupled to a variable delay element, both of whichcouple to a receiver. When operating in a calibration mode, the receiverfunctions as a phase detector and the combination of the receiver,calibration control circuit and variable delay element can effectivelyform a delay-locked loop (DLL) circuit. This DLL circuit, in response tophase information of the data signals and corresponding strobe signals,adjusts the phase relationship between the strobe signals and the datasignals for each received data bit by adjusting an offset or delay valueapplied to the strobe signal. The delay value is adjusted, for example,to optimally edge-align the data signal DQ<X> and corresponding strobesignal DQS, but is not so limited. The optimal edge-alignment can bewith respect to the rising edge or falling edge of the data DQ<X> andstrobe DQS signals. The optimal delay value, once determined, ismaintained and the system is subsequently placed in a receiver mode.

In the receiver mode, the receiver now functions as an input sampler ordata signal sampler. The delay value determined during the calibrationmode is applied to the strobe signals DQS received from the memorydevices to generate a per-bit quadrature (i.e., approximately 90 degreephase offset) sample signal DQS′ (also referred to as per-bit strobesignal DQS′); the per-bit strobe DQS′ is output for use by the inputsampler in receiving data of a corresponding data signal DQ<X>. Use ofthe delay value effectively removes the detected phase differencebetween the data signal DQ<X> and the strobe signal DQS, therebyoptimizing the overall timing margin for that specific data bit DQ<X>during data transfer operations.

In the following description, numerous specific details are introducedto provide a thorough understanding of, and enabling description for,embodiments of the strobe-offset control system. One skilled in therelevant art, however, will recognize that these embodiments can bepracticed without one or more of the specific details, or with othercomponents, systems, etc. In other instances, well-known structures oroperations are not shown, or are not described in detail, to avoidobscuring aspects of the disclosed embodiments. As an example, thestrobe-offset control embodiments described herein are presented in thecontext of transferring individual data bits DQ<X> with theunderstanding that the disclosed concepts apply to all data transferredduring memory system operations.

FIG. 1 is a block diagram of a strobe-based memory system 199 includinga strobe-offset control system 100 for individual data linestrobe-offset control, under an embodiment. The strobe-based memorysystem 199 is a component of and/or coupled to a host system or device(not shown) as appropriate to the host system/device. A strobe-offsetcontrol system 100 is coupled to receive data of each data line of thememory system 199, and can include and/or couple with additionalcomponents as appropriate to the memory system 199 or host electronicsystem. The strobe-offset control system 100 includes a receiver 102with a data input coupled to a data signal DQ<X> via a data line 104through at least one data delay element 150. The data signal DQ<X>includes information of one data bit of an N-bit wide data bytetransferred to the receiver 102 from one or more memory devices 190 viaone or more signal lines or buses 170. The receiver 102 samples the datasignal DQ<X> in response to the sample signal DQS′ 106 as describedbelow and outputs data signal 112 that includes data <0:N>.

The strobe-offset control system 100 also includes a multiplexer 140that receives a delayed strobe signal at a first input 142 and a strobesignal DQS at a second input 144. The delayed strobe signal is generatedfrom the strobe signal DQS by a strobe delay element 160. Themultiplexer 140, under control of a memory controller or other device(not shown) via a calibrate-enable signal 122, provides one of thedelayed strobe signal or the strobe signal DQS to an input 132 of avariable delay element 130 as appropriate to operating modes of thestrobe-offset control system 100 described below.

The variable delay element 130 receives the output signal of themultiplexer 140 and generates sample signals DQS′ 106 by applying adelay to the signals received at the input 132. The variable delayelement 130 of an embodiment supports delays approximately in the rangeof one-sixth (i.e., 60 degrees) to one-third (i.e., 120 degrees) of thememory system clock period, and alternative embodiments support otherdelay periods as appropriate to the receiver and the desired tuningrange of the control system 100. The variable delay element 130 outputsthe sample signal DQS′ via line 106 to the receiver 102.

The strobe-offset control system 100 also includes a calibration controlcircuit 120 which can alternatively be referred to as a calibrationcontroller 120. The calibration control circuit 120, under control of amemory controller or other device (not shown) of the memory system 199via a calibrate-enable signal 122, operates in a calibration mode toadjust an amount of the delay or offset applied by the variable delayelement 130 to versions of the strobe signal.

The calibration control circuit 120 of an embodiment uses information ofone or more signals received from the receiver 102 in performingadjustments of the variable delay value of delay element 130. One signalreceived from the receiver 102 is an adjustment control signal 114 thataffects the amount of offset applied by the variable delay element 130as described below. Further, the calibration control circuit 120receives an optional adjustment valid signal 116 from the receiver 102that indicates when information of the adjustment control signal 114 isvalid, as described below.

As described above, the strobe signal DQS is coupled to a first input ofthe multiplexer 140 using at least one strobe delay element 160. Thestrobe delay element 160 applies pre-specified delay or offset to thereceived strobe signal DQS. The strobe delay element 160 of anembodiment delays the strobe signal DQS by a period of time that isone-fourth of the memory system clock period (i.e., 90 degrees), butalternative embodiments will use delay values appropriate to thereceiver type. While the strobe delay element 160 is shown and describedas dedicated to each byte, alternative embodiments may use one strobedelay element 160 per bit.

Likewise, the data signal DQ<X> of an embodiment couples to the receiver102 through at least one data delay element 150. The data signal DQ<X>is transmitted from the memory devices 190 in a read operation, forexample. In a strobe-based system, the transmitted data signal DQ<X> isedge-aligned to the transmitted strobe signal DQS. The data delayelement 150 applies pre-specified delay to the received data signalDQ<X>, and couples a delayed version of the data signal DQ<X>′ (referredto as the delayed data signal) to the receiver 102. The data delayelement 150 delays the data signal DQ<X> by an amount that isapproximately equal to the median delay of the variable delay element130, such as one-fourth of the memory system clock period (i.e., 90degrees), but alternative embodiments will use other delay values. Thedelayed data signal DQ<X>′ is then used as a data input to the receiver102.

The memory system 199 including the strobe-offset control system 100operates in a number of modes including calibration and receiver modes.In the calibration mode the receiver 102 generally operates as a phasedetector and determines any phase difference between a delayed datasignal DQ<X>′ and the strobe signal DQS′. When operating as a phasedetector the receiver will generally be referred to herein as areceiver/phase detector 102. The receiver/phase detector 102 comparesthe phase relationship between the strobe signal DQS′ and the delayeddata signals DQ<X>′ for each received data bit, and provides thosecomparison results to the calibration control circuit 120 via theadjustment control signal 114. In response to the adjustment controlsignal 114, and optionally in additional response to the adjustmentvalid signal 116, the calibration control circuit 120 will adjust thedelay control signal 124 which affects the delay value applied to thestrobe signal DQS via the variable delay circuit 130. In thisembodiment, the receiver/phase-detector 102 in combination with thecalibration control circuit 120 and the variable delay circuit 130 actsvery much like a delay-locked loop circuit (DLL). Once this DLL-likecircuit is “locked”, the adjusted delay of the variable delay circuit130, when applied to the strobe signal DQS, results in a per-bit samplesignal DQS′ that is approximately edge-aligned to the delayed datasignal DQ<X>′. Alternatively, at least one of the delay elements 130 or150 is variable, while at most one of them is fixed, where the relativedelay between delays provided by delay elements 130 and 150 arecontrolled by the calibration control circuit 120. Furthermore, if bothdelay elements 130 and 150 are variable delay elements, calibrationcontrol circuit 120 can additionally control the absolute delay of thedelay elements 130 and 150 in addition to their relative values.

In addition to generating information representative of the offsetbetween data and data strobe signals, the calibration control circuit120 can also store the information for subsequent use and/or processing.As such, the information can be used to characterize the correspondingdata paths of the memory system. For example, the data of thischaracterization can be used to generate offsets for use by the memorycontroller in memory write operations. This data also has uses ingenerating predicted offset values for use by the variable delay element130 during calibration.

FIG. 2 is a flow diagram 200 for individual data line strobe-offsetcalibration in a calibration mode, under an embodiment. Taking one dataline as an example, a state of a calibrate-enable signal places one ormore components of the strobe-offset control system in a calibrationmode, at block 202. In the calibration mode, a multiplexer is configuredto provide the received strobe signal (DQS) to the input of a delaycircuit, at block 204. Additionally, the receiver is configured tocompare timing of the edge-positions of the delayed sample signal (DQS′)and the delayed data signals of the data line, at block 206. A dummyread of the memory devices is initiated, at block 208. A dummy read isgenerally defined to include a process in which a controller interfacecircuit makes a read request from the DRAM, independent of any dataneeds of the central processor or other higher layer machine-readablecode; these reads are performed at power-up, or other intervals in whichthe DRAM was otherwise not being utilized.

In response to the dummy read, data and DQS signals are transmitted fromthe DRAM, received at the controller, and any phase difference betweenthe delayed sample signal DQS′ and the delayed data signal is detected,at block 210. Control signals are generated in response to detectedphase differences, and the control signals are used to adjust the amountof variable delay which is applied to either the sample signal or thedata signal, at block 212. The variable delay value for each data line,when applied to a per-bit sample signal, optimally edge-aligns theper-bit sample signal to the data signal of that data line, but is notso limited. A lock signal is output in response to determination of theoptimal offset, at block 214, but generation of a lock signal isoptional as alternative embodiments can determine completion ofcalibration using any number of other methods.

Following determination and adjustment of the optimal variable delayvalue the memory system is placed in a receiver mode in which thereceiver functions as an input sampler. When operating as an inputsampler the receiver will generally be referred to herein as areceiver/input sampler 102. The variable delay value determined/adjustedduring the calibration mode is subsequently used in generating a per-bitsample signal for use by the input sampler in receiving data of acorresponding data signal. Use of the variable delay value effectivelyremoves any unwanted offsets between the data signal and the strobesignal, thereby optimizing the overall timing margin between the datasignal and the per-bit sample signal during data transfer operations.

FIG. 3 is a flow diagram 300 for receiving data signals of an individualdata line using an optimized sample signal, under an embodiment.Following calibration of the offset, as described above, a state of thecalibrate-enable signal places the strobe-offset control system in areceiver mode, at block 302. In the receiver mode, a multiplexer isconfigured to provide a delayed version of the received strobe signal(DQS) as the input to a second delay circuit, at block 304. The delayedstrobe signal is delayed by a period that is approximately one-fourth ofthe memory system clock period (i.e., 90 degrees). The output of thissecond delay circuit is provided as a sample signal for sampling datasignals of the data line, at block 306. The second delay circuit appliesan amount of delay (determined during calibration mode) to the delayedstrobe signal, at block 308 (the strobe signal, therefore, is delayed bya total period of approximately one-fourth of the memory system clockperiod plus the period of the calibrated delay). The twice delayedsignal (delayed strobe signal with calibrated applied) is subsequentlyoutput as the sample signal for sampling the individual data line, atblock 310.

As a further example of the operating modes described above, FIG. 4 is ablock diagram of a strobe-based memory system 199 including astrobe-offset control system 100 in the calibration mode, under anembodiment. The strobe-offset control system 100 and memory system 199are as described above with reference to FIG. 1. Regarding thecalibration mode, a memory controller or other component of the memorysystem 199 activates the calibrate-enable signals 122 to thestrobe-offset control system 100 in response to, for example,initialization or re-initialization of a host system. The active stateof the calibrate-enable signal 122 places the calibration controlcircuit 120 in a calibration mode, and selects the strobe signal DQS(input 144) as the output 132 of the multiplexer 140 and consequentlythe input of the variable delay element 130. The output of the variabledelay element 130 is a delayed version of the input signal, as describedbelow, and is used as a sample signal DQS′ 106 input to the receiver.

A dummy read of the memory devices 190 is then initiated by the memorycontroller (not shown) during which the delayed data signal DQ<X>′ iscompared with DQS′ by the receiver/phase detector 102. In thecalibration mode the receiver/phase detector 102 acts as a phasedetector (PD) 102 which compares the phase difference between thedelayed data signal DQ<X>′ and the sample signal DQS′. In response todetected phase differences the receiver/phase detector 102 generates anadjustment control signal 114, and an optional adjustment-valid signal116. The receiver/phase detector 102 outputs the adjustment controlsignal 114, and optionally the adjustment-valid signal 116, to thecalibration control circuit 120.

The adjustment control signal 114 is an embodiment of a delay-lockloop's (DLL's) up/down signal that the calibration controller 120 usesto affect adjustments to the delay value. The calibration controlcircuit 120 adjusts the delay applied by the variable delay element 130via signal lines 124 in response to the adjustment-control and optionaladjustment-valid signals 114 and 116. Repeated adjustments of thevariable delay value, in a closed-loop manner, results in signal DQS′106 being optimally aligned (approximately edge-aligned) to the delayeddata signal DQ<X>′.

Consequently, the combination of the receiver/phase detector 102,calibration control circuit 120 and variable delay element 130effectively form a DLL circuit. This DLL circuit, in response to phaseinformation of the delayed data signal DQ<X>′ and corresponding delayedstrobe signal DQS′, adjusts the phase relationship between these signalsfor each received data bit DQ<X> (where “X” is 0 . . . N, where “N” isthe number of bits associated with a given DQS signal) by adjusting adelay applied to the strobe signal DQS. The adjusted delay when appliedto the strobe signal DQS results in a per-bit sample signal DQS′ that isapproximately edge-aligned to the delayed data signal DQ<0>′. Anoptional lock signal 126 is subsequently output (to the memorycontroller or other circuitry of the memory system 199) by thecalibration control circuit 120 in response to determination of theedge-alignment, but alternative embodiments may not output a locksignal.

In addition to the adjustment control signal 114 described above, thereceiver/phase detector 102 of an embodiment outputs a valid signal 116to the calibration control circuit 120 of an embodiment. The validsignal 116, which is output by the receiver/phase detector 102 toindicate when the adjustment control signal 114 is valid, is used insystems in which the data pattern of the dummy read contains an unequalnumber of transitions between the data DQ<X> and strobe DQS signals.That is, while DQS is defined to transition once for every bittransmitted, the DQ<X> signal may not transition every bit (e.g., if twoor more logic-high or logic-low states are transmitted in a row). Insuch systems, the valid signal 116 indicates that the DQ<X> to DQScomparison result (i.e., adjustment control signal 114) is valid onlywhen DQ<X> is detected to have transitioned for purposes of thecomparison. Thus, the valid signal 116 may not be used in systems inwhich the data pattern of the dummy read results in an equal number oftransitions between the data DQ<X> and strobe DQS signals. Furthermore,in some embodiments the adjustment control signal 114 is the sameelectrical signal as the output of the input sampler when it is used ininput-sampler mode, i.e. data<X> signal 112.

FIG. 5 is a timing diagram 500 showing the determination/application ofthe optimal per-bit variable delay to a strobe signal DQS to generateper-bit strobe signals DQS′ during calibration mode, under anembodiment. Two data lines DQ<0> and DQ<3> are shown as examples only,as the methods described herein are similarly applied to all linesDQ<X>. Looking first at delayed data signal DQ<0>′, the rising/fallingedges of this data signal DQ<0>′ during an example dummy read(calibration mode) are offset from the corresponding rising/fallingedges of the strobe signal DQS by a first phase difference 502. Thisphase-difference will, if uncompensated for, limit the maximum bandwidthachievable by the memory system. The receiver/phase detector incombination with the calibration control circuit and variable delayelement (collectively the DLL) detects the phase difference 502, adjustsa variable delay 504 to compensate for the phase difference, and appliesthe adjusted delay 504 to the strobe signal DQS. The result of applyingthe adjusted delay 504 to the strobe signal DQS for this data line is aper-bit sample signal DQS<0>′ that is approximately edge-aligned to thedelayed data signal DQ<0>′.

Turning to a second delayed data signal DQ<3>′, the rising/falling edgesof this data signal DQ<3>′ during the example dummy read (calibrationmode) are offset from the rising/falling edges of the strobe signal DQSby a second phase difference 512. The DLL (receiver (phase detector),calibration control circuit, variable delay element) detects the phasedifference 512, adjusts a variable delay 514 to compensate for the phasedifference, and applies the adjusted delay 514 to the strobe signal DQS.The result of applying the adjusted delay 514 to the strobe signal DQSfor this data line is a per-bit sample signal DQS<3>′ that isapproximately edge-aligned to the delayed data signal DQ<3>′.

Subsequent to or simultaneous with determining an optimal amount ofvariable delay in the calibration mode, the memory system beginsoperations in the receiver mode. FIG. 6 is a block diagram of astrobe-based memory system 199 including a strobe-offset control system100 in the receiver mode, under an embodiment. The strobe-offset controlsystem 100 and memory system 199 are as described above with referenceto FIG. 1. A memory controller or other component of the memory system199 places the system in the receiver mode by deactivating thecalibrate-enable signal.

The receiver/input sampler 102 operates as an input sampler in thereceiver mode and, as such, receives a sample signal DQS′ from thevariable delay element. The sample signal is generated by the variabledelay element by applying the offset determined during the calibrationmode to the delayed strobe signal. The variable delay element outputs aper-bit sample signal DQS′ to the receiver/input sampler 102 for use insampling/receiving data of the corresponding delayed data signal DQ<X>′.The receiver/input sampler 102 outputs the sampled/received data on thedata lines 112.

FIG. 7 is a timing diagram 700 showing adjustment of strobe signaltiming using an optimal per-bit variable delay along with a fixed delayto generate a per-bit strobe signal with optimal alignment for samplinga corresponding data signal, under an embodiment. One data signal DQ<0>is shown as an example only, as the methods described herein aresimilarly applied to all data lines DQ<X>. As described above, thestrobe-offset control system receives the strobe signal DQS from thememory devices along with the data signal DQ<0>. Due to system offsetsand pin-to-pin offsets in the memory devices there is an edge-alignmentoffset 702 between the strobe signal DQS and the received data signalDQ<0>.

Applying a fixed delay 704 of approximately 90 degrees to the receiveddata signal DQ<0> as described above produces delayed data signalDQ<0>′. During the calibration mode, as described above, the delayeddata signal DQ<0>′ is compared to the received strobe signal DQS andinformation of phase/timing differences detected during this processresult in adjustment and subsequent application of a variable delay 706to the received strobe signal DQS. Application of the variable delay 706to the strobe signal DQS results in per-bit sample signal DQS<0>′(without a fixed delay). The variable delay 706 is approximately equalto the edge-alignment offset 702 plus the fixed delay 704 applied to thedata signal DQ<0>. This results in a sample signal DQS<0>′ (without afixed delay) that is approximately edge-aligned with the delayed datasignal DQ<0>′.

Following adjustment of the variable delay 706 during calibration mode,a fixed delay 708 of approximately 90 degrees is applied to the strobesignal DQS along with the variable delay 706 to generate the optimalper-bit sample signal DQS<0>′ for use by the receiver during normalreceive operations. The per-bit sample signal DQS<0>′ is optimallypositioned relative to the data signal so as to maximize the probabilityof accurately sampling the delayed data signal DQ<0>′. The amount ofper-pin offset that is correctable using the systems and methods hereinis the maximum delay difference between the delay available from thevariable delay element 130 and the data delay element 150 (FIG. 1). Theoptimal alignment provided by the systems/methods herein, therefore,overcomes some if not all effects due to system/pin-to-pin offsets.

As described above with reference to FIG. 1, the strobe-offset controlsystem 100 includes data delay elements and strobe delay elements forapplying fixed delays to the received data signals and strobe signals,respectively. The strobe-offset control system 100 of another embodimenttherefore includes one or more delay element control circuits orcontrollers for use in controlling tolerances of the delays provided bythe strobe and data delay elements.

FIG. 8 is a block diagram of a strobe-based memory system 199 includinga strobe-offset control system 800 for individual data linestrobe-offset control, under an embodiment. The delay element controlcircuit 880 generates control signals 882 for use in controlling nominalvalues of the strobe delay element 160, and/or the data delay element150, and/or the variable delay element 130. While a single delay elementcontrol circuit 880 is described below as controlling both the strobe160 and data 150 delay elements, alternative embodiments can useseparate delay element control circuit for each delay element, each typeof delay element or for different combinations of delay elements.

FIG. 9 is a block diagram of a delay element control circuit 880 for usein strobe-based memory controllers, under an embodiment. The delayelement control circuit 880 controls the respective delays or offsetswithin a pre-specified range in response to variations in operating orenvironmental parameters of the host system, memory controller, and/orstrobe-offset control system. The operating parameters include, forexample, the speed of operation, but can include numerous otherparameters as appropriate. The environmental parameters include, forexample temperature and/or power supply voltage, but can includenumerous other parameters as appropriate.

The delay element control circuit 880 of an embodiment includes a delayline 902, a phase detector 904, and a delay line controller 906. Thedelay line 902 includes four unit delay elements DE1, DE2, DE3, and DE4coupled in series and receiving the memory system clock signal 910 as aninput; alternative embodiments can include any number of unit delayelements. The delay line 902 provides a total delay that isapproximately one period of the memory system clock. Therefore, each ofthe four unit delay elements DE1-DE4 delays the input clock signal 910by an amount that is one-fourth of the memory system clock period.

The delay line output couples to the phase detector 904 along with thememory system clock signal 910. The phase detector 904 determines anyphase difference between these two input signals and outputs controlsignals 914 to the delay line controller 906 that include information ofthe detected phase difference. The delay line controller 906 in turnoutputs control signals 882 for use in controlling timing offsets of oneor more of the unit delay elements DE1-DE4 in response to theinformation from the phase detector 904. The delay line controlleroutput signals 882 are also used as control signals for use in settingthe nominal delay value of delay elements like the strobe delay element106, the data delay element 150, and the variable delay element 130. Thedelay line controller output signals 882 can be any of a variety ofsignal types known in the art, such as voltage bias signals, currentbias signals, or digital delay-control signals. The offsets of the delayelements are controlled within a pre-specified range in response tovariations in operating parameters described above.

The strobe-offset control systems described above can be used innumerous memory system types/configurations. As an alternative example,FIG. 10 is a block diagram of a strobe-offset control system 1000 forindividual data line strobe-offset control in strobe-based DDR memorysystems 1099, under an alternative embodiment of FIG. 1. As describedabove, the DDR memory system 1099 transfers data from the memory devices190 on both the rising and falling edge of the strobe signal DQS.Consequently, the DDR memory system 1099 is similar to the strobe-basedmemory system 199 described above with reference to FIG. 1 except for anadditional receiver/input sampler 102F that samples/receives data on thefalling edge of the sample signal DQS′. Likewise, the strobe-offsetcontrol system 1000 is similar to the strobe-offset control system 100described above with reference to FIG. 1 except for an additionalcoupling of the variable delay element output signal DQS′ to thefalling-edge receiver/input sampler 102F.

The strobe-based DDR memory system 1099 includes a rising-edgereceiver/input sampler 102R and a falling-edge receiver/input sampler102F both having data inputs coupled to receive a delay data signalDQ<X>′ that has been delayed by a data delay element 150. The datasignal DQ includes information of one data bit of a data bytetransferred between the receivers/input samplers 102R/102F and one ormore memory devices 190 via one or more buses 170. The rising-edgereceiver/input sampler 102R and falling-edge receiver/input sampler 102Fboth receive sample signal DQS′ from the variable delay element 130. Therising-edge receiver/input sampler 102R samples the data signal DQ<X> inresponse to the sample signal DQS′ 106 as described above and outputsdata signal 112R that includes data DATAR<0:N>. The falling-edgereceiver/input sampler 102F samples the data signal DQ<X> in response tothe sample signal DQS′ 106 as described above and outputs data signal112F that includes data DATAF<0:N>.

Components of the strobe-offset control system 1000 include acalibration control circuit 120, a variable delay element 130, and amultiplexer 140, but can include and/or couple with additionalcomponents as appropriate to the memory system 1099 or host electronicsystem. The strobe-offset control system 1000 and its various componentsoperate during data transfer operations as described above withreference to FIGS. 1-7.

Another alternative example of a strobe-offset control system providesseparate strobe-offset control for rising and falling edges of thestrobe signal DQS. FIG. 11 is a block diagram of a control system 1100for individual data line rising and falling edge strobe-offset controlin strobe-based DDR memory controllers 1199, under an alternativeembodiment of FIG. 10. As described previously, the DDR memory system1199 transfers data from the memory devices on both the rising andfalling edge of the strobe signal DQS. Consequently, the DDR memorysystem 1199 is similar to the strobe-based memory system 199 describedabove with reference to FIG. 1 except for an additional receiver. Thestrobe-based DDR memory system 1199 thus includes a rising-edgereceiver/input sampler 102R and a falling-edge receiver/input sampler102F both having data inputs coupled to receive a data signal DQ<X>′that has been delayed by a data delay element 150. The rising-edgereceiver/input sampler 102R samples data on the rising edge of a samplesignal DQS(R)′ while the falling-edge receiver/input sampler 102Fsamples data on the falling edge of a sample signal DQS(F)′. The datasignal DQ includes information of one bit of a data byte transferredbetween each of receiver/input sampler 102R/102F and one or more memorydevices (not shown). The rising-edge receiver/input sampler 102R samplesthe data signal DQ<X> in response to the sample signal DQS(R)′ asdescribed above and outputs data signal 112R that includes dataDATAR<0:N>. The falling-edge receiver/input sampler 102F samples thedata signal DQ<X> in response to the sample signal DQS(F)′ as describedabove and outputs data signal 112F that includes data DATAF<0:N>.

The strobe-offset control system 1100 is similar to the strobe-offsetcontrol system 100 described above with reference to FIG. 1 except thatit includes additional components that provide separate strobe-offsetcontrol for the rising and falling edges of the strobe signal DQS. Therising-edge strobe-offset control components (generally indicated withsuffix “R”) include a calibration or offset controller 120R, a variabledelay element 130R, and a multiplexer 140R along with correspondingsignals 132R, 124R, and 112R, as described above with reference toFIG. 1. Likewise, the falling-edge strobe-offset control components(generally indicated with suffix “F”) include a calibration or offsetcontroller 120F, a variable delay element 130F, and a multiplexer 140Falong with corresponding signals 132F, 124F, and 112F, as describedabove with reference to FIG. 1. The strobe-offset control system 1100can include and/or couple with additional components as appropriate tothe memory system 1199 or host electronic system. The strobe-offsetcontrol system 1100 operates during data transfer operations asdescribed above with reference to FIGS. 1-7.

As described above with reference to FIG. 1 for example, the calibrationcontrol circuit 120 of an embodiment uses information of one or moresignals received from the receiver 102 in performing adjustments of thevariable delay value of delay element 130. FIG. 12 is a block diagram ofa calibration control circuit 120, under an embodiment. The calibrationcontrol circuit 120 receives an up/down adjustment control signal 114that is a digital representation of the difference in phase between thestrobe signal and the data signal as detected by the receiver. Aflip-flop 1204 couples the control signal to an N-bit counter 1202, butthe embodiment is not so limited. The calibration control circuit 120can also receive an optional adjustment valid signal 116 from thereceiver that indicates when the adjustment control signal 114 is valid.The adjustment valid signal, when included, is coupled to the N-bitcounter 1202 via flip-flop 1206 in an embodiment.

In response to phase difference information of the adjustment controlsignal 114 the N-bit counter 1202 accumulates the up/down adjustment andgenerates the delay control signal 124 as appropriate to the detectedphase difference. The delay control signal 124 couples to adjust thevariable delay value of delay element 130 up or down as appropriate tothe detected phase difference.

The calibration control circuit 120 also includes optional circuitry1210 for detecting a dither condition between the phase of the strobesignal and the data signal as detected by the receiver when the phase ofthe strobe signal is approximately the same as the phase of the datasignal. In response to detecting the dither condition, the circuitry1210 enables the optional lock signal 126. The lock signal 126 issubsequently output (to the memory controller or other circuitry of thememory system 199) by the calibration control circuit 120 to indicatedetected phase alignment of the strobe and data signals.

The N-bit counter 1202 can be replaced by a charge pump in analternative embodiment of the calibration control circuit 120. As oneexample, FIG. 13 shows a charge pump 1300 that can replace the N-bitcounter 1202, under an embodiment. This charge pump 1300 includescurrent sources I1 and I2 selectively switched to a capacitor C via oneof a control (up) signal/transistor Tu or a control (down)signal/transistor Td. Alternative charge pump circuits can be used.

In operation, the calibration control circuit 120 receives an up/downadjustment control signal 114 that represents the difference in phasebetween the strobe signal and the data signal as detected by thereceiver. Information of the adjustment control signal 114 is used toprovide the control (up) signal to the gate of transistor Tu and toprovide the control (down) signal to the gate of transistor Td.

In operation, when the control (up) signal is enabled (and the control(down) signal is disabled), transistor Tu causes a first current sourceI1 to deliver charge onto capacitor C. In contrast, when the control(down) signal is enabled (and the control (up) signal is disabled),transistor Td causes a second current source 12 to sink current with asubsequent decrease in charge on capacitor C. In this manner the chargestored on the capacitor C is representative of the up or down adjustmentapplied to the variable delay value in response to the detected phasedifference between the strobe and data signals. The charge pump 1300outputs an analog control voltage V_(out) for use in generating thedelay control signal 124 (FIG. 1) as appropriate to the detected phasedifference. The delay control signal 124 couples to adjust the variabledelay value (delay element 130) up or down as appropriate to thedetected phase difference, as described above.

The components of the memory systems described above include anycollection of computing components and devices operating together. Thecomponents of the memory systems can also be components or subsystemswithin a larger computer system or network. The memory system componentscan also be coupled among any number of components (not shown), forexample other buses, controllers, memory devices, and data input/output(I/O) devices, in any number of combinations. Many of these systemcomponents may be soldered to a common printed circuit board (forexample, a graphics card or game console device), or may be integratedin a system that includes several printed circuit boards that arecoupled together in a system, for example, using connector and socketinterfaces such as those employed by personal computer motherboards anddual inline memory modules (“DIMM”). In other examples, complete systemsmay be integrated in a single package housing using a system in package(“SIP”) type of approach. Integrated circuit devices may be stacked ontop of one another and utilize wire bond connections to effectuatecommunication between chips or may be integrated on a single planarsubstrate within the package housing.

Further, functions of the memory system components can be distributedamong any number/combination of other processor-based components. Thememory systems described above include, for example, various dynamicrandom access memory (DRAM) systems. As examples, the DRAM memorysystems can include double data rate (“DDR”) systems like DDR SDRAM aswell as DDR2 SDRAM and other DDR SDRAM variants, such as Graphics DDR(“GDDR”) and further generations of these memory technologies, i.e.,GDDR2, and GDDR3, but is not limited to these memory systems.

Aspects of the system for per-bit offset control and calibrationdescribed herein may be implemented as functionality programmed into anyof a variety of circuitry, including programmable logic devices (PLDs),such as field programmable gate arrays (FPGAs), programmable array logic(PAL) devices, electrically programmable logic and memory devices andstandard cell-based devices, as well as application specific integratedcircuits (ASICs). Some other possibilities for implementing aspects ofthe per-bit offset control and calibration system include:microcontrollers with memory (such as electronically erasableprogrammable read only memory (EEPROM)), embedded microprocessors,firmware, software, etc. Furthermore, aspects of the per-bit offsetcontrol and calibration system may be embodied in microprocessors havingsoftware-based circuit emulation, discrete logic (sequential andcombinatorial), custom devices, fuzzy (neural) logic, quantum devices,and hybrids of any of the above device types. Of course the underlyingdevice technologies may be provided in a variety of component types,e.g., metal-oxide semiconductor field-effect transistor (MOSFET)technologies like complementary metal-oxide semiconductor (CMOS),bipolar technologies like emitter-coupled logic (ECL), polymertechnologies (e.g., silicon-conjugated polymer and metal-conjugatedpolymer-metal structures), mixed analog and digital, etc.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,”“comprising,” and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in a sense of “including,but not limited to.” Words using the singular or plural number alsoinclude the plural or singular number respectively. Additionally, thewords “herein,”“hereunder,”“above,”“below,” and words of similar importrefer to this application as a whole and not to any particular portionsof this application. When the word “or” is used in reference to a listof two or more items, that word covers all of the followinginterpretations of the word: any of the items in the list, all of theitems in the list and any combination of the items in the list.

The above description of illustrated embodiments of the system forper-bit offset control and calibration is not intended to be exhaustiveor to limit the system to the precise form disclosed. While specificembodiments of, and examples for, the system for per-bit offset controland calibration are described herein for illustrative purposes, variousequivalent modifications are possible within the scope of the system, asthose skilled in the relevant art will recognize. The teachings of thesystem for per-bit offset control and calibration provided herein can beapplied to other processing systems, not only for the systems describedabove.

The elements and acts of the various embodiments described above can becombined to provide further embodiments. These and other changes can bemade to the system for per-bit offset control and calibration in lightof the above detailed description.

In general, in the following claims, the terms used should not beconstrued to limit the system for per-bit offset control and calibrationto the specific embodiments disclosed in the specification and theclaims, but should be construed to include all processing systems thatoperate under the claims to provide per-bit offset control andcalibration. Accordingly, the system for per-bit offset control andcalibration is not limited by the disclosure, but instead the scope ofthe system is to be determined entirely by the claims.

While certain aspects of the system for per-bit offset control andcalibration are presented below in certain claim forms, the inventorcontemplates the various aspects of the system in any number of claimforms. For example, while only one aspect of the system is recited asembodied in computer-readable medium, other aspects may likewise beembodied in computer-readable medium. Accordingly, the inventor reservesthe right to add additional claims after filing the application topursue such additional claim forms for other aspects of the system forper-bit offset control and calibration.

1. A memory controller comprising: first and second receivers havingrespective inputs coupled in common to a first input line to receive adata signal from a memory device, the first receiver including circuitryfor sampling the data signal in response to a first sample signal and asecond receiver including circuitry for sampling the data signal inresponse to a second sample signal, wherein the first sample signal andthe second sample signal are derived from a strobe signal received fromthe memory device; a first control circuit to detect a first phasedifference between the data signal and the first sample signal and toadjust a first phase of the first sample signal in response to the firstphase difference; and a second control circuit to detect a second phasedifference between the data signal and the second sample signal and toadjust a second phase of the second sample signal, independently of thefirst phase, in response to the second phase difference.
 2. The memorycontroller of claim 1 wherein the first sample signal and the secondsample signal are delayed differently from the strobe signal.
 3. Thememory controller of claim 2 wherein the first control circuit furthercomprises a calibration control circuit coupled to receive an adjustmentcontrol signal from the first receiver and to control a propagationdelay through the first delay element to adjust the first time period inresponse to the first phase difference.
 4. The memory controller ofclaim 3 wherein the calibration control circuit comprises circuitry foroutputting a lock signal in response to determination of a targetpropagation delay.
 5. The memory controller of claim 4 wherein thecalibration control circuit further comprises circuitry for storinginformation representative of the target propagation delay.
 6. Thememory controller of claim 2 wherein the first receiver, the calibrationcontrol circuit, and the first delay element are coupled to form atleast part of a delay-locked loop (DLL) circuit.
 7. The memorycontroller of claim 2 further comprising: a first delay element to delaythe strobe signal by a first time period to generate a delayed strobesignal; a first multiplexer to receive the strobe signal and the delayedstrobe signal and to output the first timing signal, the first samplesignal being derived from the first timing signal; and a secondmultiplexer to receive the strobe signal and the delayed strobe signaland to output a second timing signal, the second sample signal beingderived from the second timing signal.
 8. The memory controller of claim7 wherein the first multiplexer comprises circuitry to receive a firstmode control signal, wherein the first mode control signal selects oneof the strobe signal and the delayed strobe signal to be output as thefirst timing signal.
 9. The memory controller of claim 8 wherein thefirst mode control signal selects the delayed strobe signal to be outputas the first timing signal when the memory controller is in a receivemode, and wherein the mode control signal selects the strobe signal tobe output as the first timing signal when the memory controller is in acalibration mode.
 10. The memory controller of claim 9 wherein the firstreceiver functions as an input sampler when the memory controller is inthe receive mode and wherein the first receiver functions as an inputsampler when the memory controller is in the calibration mode.
 11. Thememory controller of claim 8 wherein the first calibration controlcircuit further comprises circuitry to receive the first mode controlsignal.
 12. The memory controller of claim 1 wherein the first receivercomprises circuitry for sampling the data signal in response to a risingedge of the first sample signal and the second receiver comprisescircuitry for sampling the data signal in response to a falling edge ofthe second sample signal.
 13. The memory controller of claim 1 furthercomprising a delay element to delay the data signal by a time period.14. The memory controller of claim 13 wherein the delay element iscoupled to receive the data signal from the memory device and to outputthe data signal to the first receiver.
 15. The memory controller ofclaim 1, wherein the memory device is a Double Data Rate (DDR) device.16. A method of performing timing calibration in a memory system, themethod comprising: receiving a data signal from a memory device via afirst input line; detecting a first phase difference between the datasignal and a first sample signal, wherein the first sample signalderived from a strobe signal; detecting a second phase differencebetween the data signal and a second sample signal, wherein the secondsample signal is derived from the strobe signal; adjusting a first phaseof the first sample signal in response to the first phase difference;and adjusting a second phase of the second sample signal in response tothe second phase difference.
 17. The method of claim 16 furthercomprising: generating the first sample signal by applying a first phaseoffset to a first timing signal; and generating the second sample signalby applying a second phase offset to a second timing signal.
 18. Themethod of claim 17 further comprising: receiving the strobe signal fromthe memory device; receiving a first mode control signal and a secondmode control signal; generating the first timing signal by selectivelyapplying a third phase offset to the strobe signal in response to thefirst mode control signal; and generating the second timing signal byselectively applying the third phase offset to the strobe signal inresponse to the second mode control signal.
 19. The method of claim 16further comprising adjusting a third phase offset of the data signal.20. An offset control system comprising: means for detecting a firstphase difference between a data signal and a first sample signal, thedata signal being received from a memory device via a first input line,wherein the first sample signal is derived from a strobe signal; meansfor detecting a second phase difference between the data signal and asecond sample signal, wherein the second sample signal is derived fromthe strobe signal; means for adjusting a first phase of the first samplesignal in response to the first phase difference; means for adjusting asecond phase of the second sample signal in response to the second phasedifference; means for generating the first sample signal by applying afirst phase offset to a first timing signal; and means for generatingthe second sample signal by applying a second phase offset to a secondtiming signal.